Work vehicle control system, work vehicle control method, and work vehicle

ABSTRACT

A control system for a work vehicle, which includes a vehicle body and work equipment that is changeable in height and pitch with respect to the vehicle body, includes a controller. The controller determines a switching point by referring to target displacement data indicating a target displacement of the height of the work equipment according to a movement amount of the work vehicle from a work start position. The controller determines whether or not the work vehicle has reached the switching point based on the movement amount of the work vehicle from the work start position. The controller outputs a command to change the pitch of the work equipment upon determining that the work vehicle has reached the switching point.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National stage application of International Application No. PCT/JP2021/037638, filed on Oct. 11, 2021. This U.S. National stage application claims priority under 35 U.S.C. § 119(a) to Japanese Patent Application No. 2020-171979, filed in Japan on Oct. 12, 2020, the entire contents of which are hereby incorporated herein by reference.

The present disclosure relates to a control system for a work vehicle, a method for controlling a work vehicle, and a work vehicle.

BACKGROUND INFORMATION

Japanese Unexamined Patent Application, First Publication No. H07-252859 discloses a technique related to a bulldozer that improves the efficiency of excavation, transport, and dumping by switching the pitch angle of a blade. According to Japanese Unexamined Patent Application, First Publication No. H07-252859, the pitch angle of the blade can be changed by tilting an operation lever with a tilt and pitch changeover switch turned on.

SUMMARY

On the other hand, when the pitch angle of the blade is manually adjusted as in the technique described in Japanese Unexamined Patent Application, First Publication No. H07-252859, if an operator erroneously sets an operation timing or an operation amount, there is a possibility that work efficiency decreases.

An object of the present disclosure is to provide a control device for a work vehicle and a method for controlling a work vehicle that automatically control the pitch of a blade according to a working state of the work vehicle.

According to a first aspect of the present disclosure, there is provided a control system for a work vehicle including a vehicle body and work equipment that is changeable in height and pitch with respect to the vehicle body, the system including a controller. The controller determines a switching point by referring to target displacement data indicating a target displacement of the height of the work equipment according to a movement amount of the work vehicle from a work start position. The controller determines whether or not the work vehicle has reached the switching point, based on the movement amount of the work vehicle from the work start position. The controller outputs a command to change the pitch of the work equipment when it is determined that the work vehicle has reached the switching point.

According to a second aspect of the present disclosure, there is provided a method for controlling a work vehicle including a vehicle body and work equipment that is changeable in height and pitch with respect to the vehicle body, the method including the following processes. A first process is to determine a switching point by referring to target displacement data indicating a target displacement of the height of the work equipment according to a movement amount of the work vehicle from a work start position. A second process is to determine whether or not the work vehicle has reached the switching point, based on the movement amount of the work vehicle from the work start position. A third process is output a command to change the pitch of the work equipment when it is determined that the work vehicle has reached the switching point.

According to a third aspect of the present disclosure, there is provided a work vehicle including: a vehicle body; work equipment configured to be changeable in height and pitch with respect to the vehicle body; and a controller. The controller determines a switching point by referring to target displacement data indicating a target displacement of the height of the work equipment according to a movement amount of the work vehicle from a work start position. The controller determines whether or not the work vehicle has reached the switching point, based on the movement amount of the work vehicle from the work start position. The controller outputs a command to change the pitch of the work equipment so as to tilt the work equipment rearward with respect to the vehicle body, when it is determined that the work vehicle has reached the switching point.

According to the aspects, the control device can automatically control the pitch of the blade according to a working state of the work vehicle.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side view of a work vehicle according to a first embodiment.

FIG. 2 is a view showing a posture of a blade according to the first embodiment.

FIG. 3 is a block diagram showing a configuration of a drive system and a control system for the work vehicle according to the first embodiment.

FIG. 4 is a schematic block diagram showing a configuration of a controller of the work vehicle according to the first embodiment.

FIG. 5 is a flowchart showing a control process of work equipment according to the first embodiment.

FIG. 6 is a view showing an example of a final design topography, a current topography, and a target design topography according to the first embodiment.

FIG. 7 is a view showing an example of target displacement data according to the first embodiment.

FIG. 8 is a flowchart showing a process of determining a target displacement according to the first embodiment.

FIG. 9 is a view showing a change in the height of the blade according to the first embodiment.

FIG. 10 is a block diagram showing a configuration of a drive system and a control system according to a first modification example.

FIG. 11 is a block diagram showing a configuration of a drive system and a control system according to a second modification example.

DESCRIPTION OF EMBODIMENTS First Embodiment

Hereinafter, embodiments will be described in detail with reference to the drawings.

FIG. 1 is a side view of a work vehicle 100 according to a first embodiment.

The work vehicle 100 according to the first embodiment is, for example, a bulldozer. The work vehicle 100 includes a vehicle body 110, a travel device 120, and work equipment 130.

The vehicle body 110 includes a cab 140. The cab 140 is provided on an upper portion of the vehicle body 110. A driver's seat (not shown) is disposed in the cab 140. The travel device 120 is provided on a lower portion of the vehicle body 110. The travel device 120 includes a pair of left and right crawler belts 121, sprockets 122, and idlers 124. Incidentally, only the left crawler belt 121, the left sprocket 122, and the left idler 124 are shown in FIG. 1 . As the crawler belts 121 rotate, the work vehicle 100 travels. The travel of the work vehicle 100 may be any form of autonomous travel, semi-autonomous travel, and travel under operation by the operator. A rotation sensor 123 is provided on a rotating shaft of the sprockets 122. The rotation sensor 123 measures a rotation speed of the rotating shaft of the sprockets 122. The rotation speed of the rotating shaft of the sprocket 122 can be converted into a speed of the travel device 120 and into a movement amount of the vehicle body 110.

The work equipment 130 is used to excavate and transport an excavation target such as earth. The work equipment 130 is provided at a front portion of the vehicle body 110. The work equipment 130 includes a lift frame 131, a blade 132, a lift cylinder 133, and a pitch cylinder 134.

The lift frame 131 is attached to a side surface of the vehicle body 110 via a pin extending in a vehicle width direction. The lift frame 131 is supported to be rotatable about an axis X1 in an up-down direction with respect to the vehicle body 110, the axis X1 extending in the vehicle width direction. The lift frame 131 supports the blade 132.

The blade 132 is attached to the front of the vehicle body 110 via the lift frame 131. The blade 132 is supported to be rotatable about an axis X2 with respect to the lift frame 131, the axis X2 extending in the vehicle width direction. The blade 132 moves up and down with an up and down movement of the lift frame 131. A bucket blade edge 132 e is provided at a front lower end portion of the blade 132.

The lift cylinder 133 is a hydraulic cylinder. The lift cylinder 133 is connected to the vehicle body 110 and to the blade 132. As the lift cylinder 133 extends and contracts, the lift frame 131 and the blade 132 rotate about the axis X1 in the up-down direction.

The pitch cylinder 134 is a hydraulic cylinder. The pitch cylinder 134 is connected to the lift frame 131 and to the blade 132. As the pitch cylinder 134 extends and contracts, the blade 132 rotates about the axis X2 with respect to the lift frame 131. More specifically, the extension of the pitch cylinder 134 causes the blade 132 to tilt about the axis X2 to the forward of the vehicle body with respect to the lift frame 131 (pitch dump). As the pitch cylinder 134 contracts, the blade 132 tilts about the axis X2 to the rearward of the vehicle body with respect to the lift frame 131 (pitch back).

FIG. 2 is a view showing a posture of the blade 132 according to the first embodiment. The blade 132 is switched between an excavation posture, a transport posture, and a dump posture by a controller 320 to be described later. The excavation posture is a posture in which the angle of the bucket blade edge of the blade 132 is set to a first angle (for example, 52 degrees) with respect to a bottom surface of the crawler belt 121. The transport posture is a posture in which the angle of the bucket blade edge of the blade 132 is set to a second angle by tilting the blade 132 to the rearward of the vehicle body to the maximum extent. The dump posture is a posture in which the angle of the bucket blade edge of the blade 132 is set to a third angle by tilting the blade 132 to the forward of the vehicle body. The first angle is larger than the second angle, and is smaller than the third angle.

FIG. 3 is a block diagram showing a configuration of a drive system 200 and a control system 300 for the work vehicle 100 according to the first embodiment.

<<Drive System 200>>

The drive system 200 includes a power source 210, a power take off (PTO) 220, a power transmission device 230, and a hydraulic pump 240.

The power source 210 is, for example, a diesel engine.

The PTO 220 transmits some of a driving force of the power source 210 to the hydraulic pump 240. Namely, the PTO 220 distributes the driving force of the power source 210 to the power transmission device 230 and to the hydraulic pump 240.

The power transmission device 230 transmits the driving force of the power source 210 to the travel device 120. The power transmission device 230 may be, for example, a hydrostatic transmission (HST). Alternatively, the power transmission device 230 may be, for example, a torque converter, a transmission including a plurality of speed change gears, a hydraulic mechanical transmission (HMT), or an electric transmission device in which a generator and a driving electric motor are combined.

The hydraulic pump 240 is driven by the power source 210, to discharge a hydraulic oil. The hydraulic oil discharged from the hydraulic pump 240 is supplied to the lift cylinder 133 and to the pitch cylinder 134 via a control valve 330. The control valve 330 controls the flow rate of the hydraulic oil discharged from the hydraulic pump 240.

<<Control System 300>>

The control system 300 includes an operation device 310, the controller 320, and the control valve 330.

The operation device 310 is a device for operating the work equipment 130 and the travel device 120. The operation device 310 is disposed in the cab 140. The operation device 310 receives an operation for driving the work equipment 130 and the travel device 120 input by the operator, and outputs an operation signal according to the operation. The operation device 310 includes, for example, operation levers, pedals, switches, and the like.

The operation device 310 includes a pitch operation switch 312 for controlling the pitch of the blade 132. The pitch operation switch 312 is, for example, a momentary switch that is operable between a pitch-dump position and a pitch-back position. An operation signal of the pitch operation switch 312 is output to the controller 320. In response to the operation signal from the pitch operation switch 312, the controller 320 outputs a command signal for controlling the pitch cylinder 134 to rotate the blade 132 about the axis X2 with respect to the lift frame 131, to the control valve 330. When the operation position of the pitch operation switch 312 is at the pitch-dump position, the controller 320 controls the control valve 330 to tilt the blade 132 to the forward of the vehicle body. When the operation position of the pitch operation switch 312 is at the pitch-back position, the controller 320 controls the control valve 330 to tilt the blade 132 to the rearward of the vehicle body. Incidentally, the pitch operation switch 312 may be formed of two push buttons of which each outputs one of a pitch-dump operation signal and a pitch-back operation signal.

The controller 320 controls the work vehicle 100. The controller 320 automatically controls the work equipment 130 according to a program to be described later based on a current topography of a construction site, a final design surface, and measurement values of various sensors.

The control valve 330 is a proportional control valve, and is controlled by a command signal from the controller 320. The control valve 330 is disposed between the hydraulic pump 240 and a hydraulic actuator, such as the lift cylinder 133 or the pitch cylinder 134. The control valve 330 controls the flow rate of the hydraulic oil to be supplied from the hydraulic pump 240 to the lift cylinder 133 and to the pitch cylinder 134. The controller 320 generates a command signal to the control valve 330 to operate the blade 132 according to the operation of the operation device 310 described above. Accordingly, the lift cylinder 133 and the pitch cylinder 134 are controlled according to an operation amount of the operation device 310. Incidentally, the control valve 330 may be a pressure proportional control valve. Alternatively, the control valve 330 may be an electromagnetic proportional control valve.

The control system 300 includes a stroke sensor 133 s. The stroke sensor 133 s detects a stroke amount of the lift cylinder 133. A position of the bucket blade edge 132 e in a vehicle body coordinate system that is a local coordinate system with reference to the vehicle body 110 can be calculated by using the stroke amount detected by the stroke sensor 133 s. Specifically, the controller 320 calculates a rotation angle of the lift frame 131 based on the stroke amount of the lift cylinder 133. Since the dimensions of the lift frame 131 and the blade 132 are already known, the position of the bucket blade edge 132 e of the blade 132 can be specified from the rotation angle of the lift frame 131. Incidentally, the work vehicle 100 according to other embodiments may detect a rotation angle using other sensors, such as an encoder.

As shown in FIG. 3 , the control system 300 includes a position detection device 340. The position detection device 340 measures a position of the work vehicle 100. The position detection device 340 includes a global navigation satellite system (GNSS) receiver 341 and an inertial measurement unit (IMU) 342. The GNSS receiver 341 is, for example, a global positioning system (GPS) receiver. An antenna of the GNSS receiver 341 is attached onto, for example, the cab 140. The GNSS receiver 341 receives positioning signals from satellites, and computes a position of the antenna from the positioning signals to generate vehicle position data. The GNSS receiver 341 outputs the position data of the work vehicle 100 to the controller 320.

The IMU 342 acquires vehicle body tilt angle data and vehicle body acceleration data. The vehicle body tilt angle data includes an angle with respect to the horizontal in a vehicle front-rear direction (pitch angle), and an angle with respect to the horizontal in a vehicle lateral direction (roll angle). The vehicle body acceleration data includes an acceleration of the work vehicle 100. The IMU 342 outputs the vehicle body tilt angle data and the vehicle body acceleration data to the controller. The controller 320 obtains a traveling direction and a vehicle speed of the work vehicle 100 from the vehicle body acceleration data.

FIG. 4 is a schematic block diagram showing a configuration of the controller 320 of the work vehicle 100 according to the first embodiment. The controller 320 is a computer including a processor 321, a main memory 322, a storage 323, and an interface 324. The processor 321 performs computational processing of operation of the work equipment 130 by executing the program.

The main memory 322 stores design topography data and worksite topography data. The design topography data indicates a final design topography. The final design topography is a final target shape of a surface of a worksite. The design topography data is, for example, a civil engineering construction drawing in a three-dimensional data format. The worksite topography data indicates a current topography of the worksite. The worksite topography data is, for example, a current topographical survey map in a three-dimensional data format. The worksite topography data can be obtained, for example, by an aerial laser survey.

The storage 323 is a non-transitory storage medium. Exemplary examples of the storage 323 include magnetic disks, magneto-optical disks, semiconductor memories, and the like. The storage 323 may be an internal medium directly connected to a bus of the controller 320, or may be an external medium connected to the controller 320 via the interface 324 or via a communication line. The storage 323 stores the program for controlling the work vehicle 100.

Incidentally, in embodiments, the controller 320 may include a custom large scale integrated circuit (LSI), such as a programmable logic device (PLD), in addition to the above configuration or instead of the above configuration. Exemplary examples of the PLD include a programmable array logic (PAL), a generic array logic (GAL), a complex programmable logic device (CPLD), and a field programmable gate array (FPGA). In this case, some or all of the functions to be realized by the processor 321 may be realized by the integrated circuit.

<<Operation of Work Vehicle 100>>

Hereinafter, control of the work equipment 130 for excavation executed by the controller 320 will be described. FIG. 5 is a flowchart showing a control process of the work equipment 130 according to the first embodiment. When the work vehicle 100 starts working, the posture of the blade 132 is the excavation posture.

As shown in FIG. 5 , in step S1, the controller 320 acquires current position data from the position detection device 340.

In step S2, the controller 320 acquires design topography data of a construction site. As shown in FIG. 6 , the design topography data includes heights Zdesign of a final design topography 60 at a plurality of reference points in a traveling direction of the work vehicle 100. The plurality of reference points indicate a plurality of points at predetermined intervals along the traveling direction of the work vehicle 100. The plurality of reference points are on a traveling path of the blade 132. Incidentally, in FIG. 6 , the final design topography 60 has a flat shape parallel to a horizontal direction, but may have a different shape. The design topography data may be acquired via the interface 324, may be acquired via an external storage device, or may be acquired from another device connected via a network. The controller 320 stores the design topography data in the main memory 322.

In step S3, the controller 320 acquires current topography data of the construction site. The controller 320 computationally acquires the current topography data from the worksite topography data obtained from the main memory 322 and position data and traveling direction data of the vehicle body obtained from the position detection device 340. The current topography data is information indicating a topography located in the traveling direction of the work vehicle 100. FIG. 6 shows a cross-section of a current topography 50. Incidentally, in FIG. 6 , the vertical axis indicates the height of the topography, and the horizontal axis indicates the distance from a current position in the traveling direction of the work vehicle 100.

In step S4, the controller 320 acquires a work start position. For example, the controller 320 calculates a position of the bucket blade edge 132 e of the blade 132 in a site coordinate system based on a measurement value of the stroke sensor 133 s and on a measurement value of the position detection device 340, and acquires a position where the position of the bucket blade edge 132 e is initially below a height of the current topography, as an excavation start position. However, the controller 320 may acquire the excavation start position through other methods. For example, the controller 320 may acquire the excavation start position based on operation of a work equipment operation device 311. For example, the controller 320 may acquire the excavation start position based on operation of a button or an operation, such as a screen operation of a touch panel.

In step S5, the controller 320 acquires a movement amount of the work vehicle 100. The controller 320 acquires a distance traveled from the excavation start position to a current position on the traveling path of the blade 132, as the movement amount. The movement amount of the work vehicle 100 may be the movement amount of the vehicle body 110. Alternatively, the movement amount of the work vehicle 100 may be the movement amount of the bucket blade edge 132 e.

In step S6, the controller 320 determines target design topography data. The target design topography data indicates a target design topography 70 indicated by a broken line in FIG. 6 . The target design topography 70 indicates the desired trajectory of the bucket blade edge 132 e of the blade 132 during work. The target design topography 70 is a topographical profile desired as a result of excavation work. As shown in FIG. 6 , the controller 320 determines a displacement distance ΔZ from and the target design topography 70 displaced downward from the current topography 50. The displacement distance ΔZ is a target displacement in a vertical direction at each reference point. In the present embodiment, the displacement distance ΔZ is a target depth at each reference point, and indicates the target position of the blade 132 below the current topography 50. The target position of the blade 132 means the position of the bucket blade edge 132 e of the blade 132. In other words, the displacement distance ΔZ indicates the earth amount per unit movement amount excavated by the blade 132. Therefore, the target design topography data indicates a relationship between the plurality of reference points and a plurality of target earth amounts. Incidentally, the controller 320 determines the target design topography 70 so as not to go below the final design topography 60. Therefore, the controller 320 determines the target design topography 70 in which the target heights are located on the final design topography 60 or higher and below the current topography 50.

Specifically, the controller 320 determines a height Z of the target design topography 70 using the following Equation (1).

Z=Zm−ΔZ

ΔZ=t1*t2*Z_offset  [Equation 1]

Zm (m=1, . . . , n) are heights Z0 to Zn of the current topography 50 at the plurality of reference points. ΔZ is a displacement distance, and indicates an excavation depth in FIG. 6 . t1 is a scaling factor based on tractive force data indicating magnitudes of tractive forces useable by the work vehicle.

t2 is a scaling factor according to blade specification data. The blade specification data is determined according to the specifications of the selected blade.

Z_offset is a target displacement determined according to a movement amount of the work vehicle 100. The target displacement Z_offset is one example of a target load parameter related to a load on the blade 132. The target displacement Z_offset indicates a displacement amount of the blade 132 from the ground surface in a height direction (vertical direction). FIG. 7 is a view showing one example of target displacement data C. The target displacement data C represents the excavation depth (target displacement) Z_offset of the blade 132 from the ground surface in a vertical downward direction as a dependent variable of a movement amount n of the work vehicle 100 in the horizontal direction. The movement amount n of the work vehicle 100 in the horizontal direction is substantially the same value as a movement amount of the blade 132 in the horizontal direction. The controller 320 determines the target displacement Z_offset from the movement amount n of the work vehicle 100 by referring to the target displacement data C shown in FIG. 7 .

As shown in FIG. 7 , the target displacement data C defines a relationship between the movement amount n of the work vehicle 100 and the target displacement Z_offset. The target displacement data C is stored in the main memory 322. Hereinafter, for simplicity of description, it is assumed that the values of t1 and t2 are 1 and the displacement distance ΔZ is equal to the target displacement Z_offset.

As shown in FIG. 7 , the target displacement data C includes data c1 at start, data c2 during excavation, data c3 during transition, and data c4 during transport. The data c1 at start defines a relationship between the movement amount n and the target displacement Z_offset in an excavation start region. The excavation start region is a region from an excavation start point S to a steady excavation start point D. As indicated by the data c1 at start, the target displacement Z_offset that gradually increases with an increase in the movement amount n is defined in the excavation start region. The data c1 at start defines the target displacement Z_offset that linearly increases with respect to the movement amount n.

The data c2 during excavation defines a relationship between the movement amount n and the target displacement Z_offset in an excavation region. The excavation region is a region from the steady excavation start point D to a transport transition start point T. As indicated by the data c2 during excavation, the target displacement Z_offset is defined as a constant value in the excavation region. The data c2 during excavation defines the target displacement Z_offset that is constant with respect to the movement amount n.

The data c3 during transition defines a relationship between the movement amount n and the target displacement Z_offset in a transport transition region. The transport transition region is a region from the transport transition start point T to a transport start point P. As indicated by the data c3 during transition, the target displacement Z_offset that gradually decreases with an increase in the movement amount n is defined in the transport transition region. The data c3 during transition defines the target displacement Z_offset that linearly decreases with respect to the movement amount n.

The data c4 during transport defines a relationship between the movement amount n and the target displacement Z_offset in a transport region. The transport region is a region that starts from the transport start point P. As indicated by the data c4 during transport, the target displacement Z_offset is defined as a constant value in the transport region. The data c4 during transport defines the target displacement Z_offset that is constant with respect to the movement amount n.

Specifically, the excavation region starts from a first start value b1 and ends at a first end value b2. The transport region starts from a second start value b3. The first end value b2 is smaller than the second start value b3. Therefore, the excavation region starts when the movement amount n is smaller than that of the transport region. The target displacement Z_offset in the excavation region is constant at a first target value a1. The target displacement Z_offset in the transport region is constant at a second target value a2. The first target value a1 is larger than the second target value a2. Therefore, the displacement distance ΔZ is defined as being larger in the excavation region than in the transport region.

The target displacement Z_offset at the excavation start position is a start value a0. The start value a0 is smaller than the first target value a1. In the example shown in FIG. 7 , the start target value a0 is smaller than the second target value a2.

FIG. 8 is a flowchart showing a process of determining the target displacement Z_offset. For simplicity of description, in the determination process to be described below, it is assumed that the work vehicle 100 travels only forward. The determination process is started when the operation device 310 for operating the travel device 120 moves to a forward travel position. In step S201, the controller 320 determines whether or not the movement amount n is 0 or greater and less than the first start value b1. When the movement amount n is 0 or greater and less than the first start value b1, in step S202, the controller 320 gradually increases the target displacement Z_offset from the start value a0 with an increase in the movement amount n.

The start value a0 is a constant and is stored in the main memory 322. It is preferable that the start value a0 is such a small value that a load on the blade 132 at the start of excavation is not too large. The first start value b1 is computationally obtained from a slope c1 in the excavation start region, the start value a0, and the first target value a1 shown in FIG. 7 . The slope c1 is a constant and is stored in the main memory 322. It is preferable that the slope c1 is set to such a value that a rapid transition can be made from the start of excavation to excavation work and a load on the blade 132 is not too large.

In step S203, the controller 320 determines whether or not the movement amount n is the first start value b1 or greater and less than the first end value b2. When the movement amount n is the first start value b1 or greater and less than the first end value b2, in step S204, the controller 320 sets the target displacement Z_offset to the first target value a1. The first target value a1 is a constant and is stored in the main memory 322. It is preferable that the first target value a1 is such a value that excavation can be efficiently performed and a load on the blade 132 is not too large.

In step S205, the controller 320 determines whether or not the movement amount n is the first end value b2 or greater and less than the second start value b3. When the movement amount n is the first end value b2 or greater and less than the second start value b3, in step S206, the controller 320 gradually reduces the target displacement Z_offset from the first target value a1 with an increase in the movement amount n.

The first end value b2 is a movement amount when a current earth amount held by the blade 132 is greater than a predetermined threshold value. Therefore, when the current earth amount held by the blade 132 is greater than the predetermined threshold value, the controller 320 reduces the target displacement Z_offset from the first target value a1. The predetermined threshold value is determined based on, for example, a maximum capacity of blade 132. For example, a load on the blade 132 may be measured, and the current earth amount held by the blade 132 may be computationally determined from the load. Alternatively, an image of the blade 132 may be captured by a camera, and the current earth amount held by the blade 132 may be calculated by analyzing the image. Alternatively, point cloud data of the blade 132 may be acquired by a scanner, and the current earth amount held by the blade 132 may be calculated by analyzing the point cloud data.

Incidentally, at the start of work, a predetermined initial value is set to the first end value b2. After the start of work, a movement amount when the earth amount held by the blade 132 is greater than the predetermined threshold value is stored as an update value, and the first end value b2 is updated based on the stored update value.

In step S207, the controller 320 determines whether or not the movement amount n is equal to or greater than the second start value b3. When the movement amount n is equal to or greater than the second start value b3, in step S208, the controller 320 sets the target displacement Z_offset to the second target value a2.

The second target value a2 is a constant and is stored in the main memory 322. It is preferable that the second target value a2 is set to a value suitable for transport work. For example, the second target value a2 may be set such that the target displacement Z_offset in the transport region is 0. Namely, the second target value a2 may be a value equal to or less than the initial target value a0. The second start value b3 is computationally obtained from a slope c3 in the transport transition region, the first target value a1, and the second target value a2 shown in FIG. 7 . The slope c3 is a constant and is stored in the main memory 322. It is preferable that the slope c3 is set to such a value that a rapid transition can be made from the excavation work to transport work and a load on the blade 132 is not too large.

Incidentally, the start value a0, the first target value a1, and the second target value a2 may be changed according to situations of the work vehicle 100 or the like. The first start value b1, the first end value b2, and the second start value b3 may be stored in the main memory 322 as constants.

As described above, the height Z of the target design topography 70 is determined by determining the target displacement Z_offset.

In step S7, the controller 320 controls the work equipment 130 to move toward the target design topography 70. Here, the controller 320 generates a command signal to the work equipment 130 to move the position of the bucket blade edge 132 e of the blade 132 toward the target design topography 70 created in step S6. The generated command signal is input to the control valve 330. Accordingly, the bucket blade edge 132 e of the blade 132 moves along the target design topography 70.

In the excavation region described above, the displacement distance ΔZ between the current topography 50 and the target design topography 70 is larger than in the other regions. Accordingly, in the excavation region, excavation work of the current topography 50 is performed. In the transport region, the displacement distance ΔZ between the current topography 50 and the target design topography 70 is smaller than in the other regions. Accordingly, in the transport region, the ground surface is refrained from being excavated, and earth held by the blade 132 is transported.

In step S8, the controller 320 determines whether or not the work vehicle 100 has reached a switching point, based on the movement amount acquired in step S5, or whether or not the pitch operation switch 312 has been continuously operated to the pitch-back position for a certain period of time by the operator. The switching point is one of a point apart from the excavation start point by a first distance, a point apart from the excavation start point by a second distance, and a point apart from the excavation start point by a third distance. The switching point can be appropriately selected by the operator. As shown in FIG. 7 , the point apart from the excavation start point by the first distance corresponds to the steady excavation start point D. In addition, the point apart from the excavation start point by the second distance corresponds to the transport transition start point T. In addition, the point apart from the excavation start point by the third distance corresponds to the transport start point P. A determination reference position is the position of the center of gravity of the vehicle body 110 or the position of the bucket blade edge 132 e.

When the determination reference position has not reached the switching point and the pitch operation switch 312 has not been continuously operated to the pitch-back position for the certain period of time (step S8: NO), in step S9, the controller 320 controls the work equipment 130 to move toward the target design topography 70. Here, a command signal to the work equipment 130 is generated to move the position of the bucket blade edge 132 e of the blade 132 toward the target design topography 70 created in step S6. The generated command signal is input to the control valve 330. Accordingly, the position of the bucket blade edge 132 e of the work equipment 130 moves along the target design topography 70.

On the other hand, when the determination reference position has reached the switching point or the pitch operation switch 312 has been continuously operated to the pitch-back position for the certain period of time (step S8: YES), in step S10, the controller 320 generates a command signal to the work equipment 130 to cause the blade 132 to assume the transport posture. Here, a command signal for controlling the pitch cylinder 134 to cause the blade 132 to assume the transport posture is generated. For example, since the transport posture is a posture in which the blade 132 is tilted to the rearward of the vehicle body to the maximum extent, the controller 320 may output a command signal to the control valve 330 until a predetermined time elapses after the discharge pressure of the hydraulic pump 240 has become equal to or greater than the relief pressure of the pitch cylinder 134.

In step S11, the controller 320 controls the lift cylinder 133 to cause the blade 132 to move toward the target design topography 70. FIG. 9 is a view showing a change in the height of the blade according to the first embodiment. A state ST_A indicates a state where the blade 132 is placed in the excavation posture and the bucket blade edge 132 e is aligned with a reference height H0. In the state ST_A, when the pitch cylinder 134 extends to cause the blade 132 to perform pitch dump, the work vehicle 100 is brought into a state ST_B where the blade 132 rotates about the axis X2 and the height of the bucket blade edge 132 e is lower than the reference height H0.

In the state ST_A, when the pitch cylinder 134 contracts to cause the blade 132 to perform pitch back, the work vehicle 100 is brought into a state ST_C where the blade 132 rotates about the axis X2 and the height of the bucket blade edge 132 e is higher than the reference height H0. Therefore, in step S11, the controller 320 generates a control signal to the lift cylinder 133 to move the position of the bucket blade edge 132 e of the blade 132 toward the target design topography 70 while canceling out a change in the height of the bucket blade edge caused by the driving of the pitch cylinder 134. Incidentally, the amount of the change in the height of the bucket blade edge caused by the driving of the pitch cylinder 134 can be specified by dimension data of the work equipment 130.

In step S12, the controller 320 updates the worksite topography data. The controller 320 acquires position data indicating the latest trajectory of the bucket blade edge 132 e, as current topography data, and updates the worksite topography data with the acquired current topography data. Alternatively, the controller 320 may calculate a position of the bottom surface of the crawler belt 121 from vehicle body position data and vehicle body dimension data, and acquire position data indicating a trajectory of the bottom surface of the crawler belt 121, as current topography data. In this case, the updating of work topography data can be immediately performed.

As described above, the controller 320 according to the first embodiment determines a switching point by referring to the target displacement data indicating the target displacement of the height of the work equipment according to a movement amount of the work vehicle from the work start position. In addition, it is determined whether or not the work vehicle 100 has reached the switching point, and when it is determined that the work vehicle 100 has reached the switching point, the work equipment 130 is tilted to the rearward of the vehicle body. Accordingly, the controller 320 automatically causes the blade 132 to perform a pitch operation during transition from excavation work to transport work, so that a work burden on the operator can be reduced. In addition, the controller 320 controls the pitch of the blade 132 and also controls the height of the blade 132, so that earth can be prevented from being spilled during transition from excavation work to transport work. In addition, the controller 320 changes the pitch angle of the blade 132 at an optimum timing, so that the earth amount during transport can be maximized, and work efficiency can be improved.

In addition, according to the first embodiment, the operator sets the switching point to the point apart from the excavation start point by the first distance, the point apart from the excavation start point by the second distance, or the point apart from the excavation start point by the third distance, and sets the determination reference position to that of the bucket blade edge 132 e of the blade 132 or of the center of gravity of the vehicle body 110. Accordingly, the operator can set a control timing of the pitch angle of the blade 132 to a timing suitable for earth quality of a work target and for operation feeling of the operator. For example, depending on earth quality, if the blade 132 remains in the excavation posture when the blade 132 is lifted up, the blade 132 may be pressed against the work target, and excavation may not be efficiently performed. In such a case, the pitch angle of the blade 132 can be controlled at a proper timing by setting the switching point to the point apart from the excavation start point by the second distance, and by setting the determination reference position to that of the bucket blade edge 132 e of the blade 132. Incidentally, in other embodiments, setting by the operator may not need to be received by setting the switching point to the point apart from the excavation start point by the first distance, the point apart from the excavation start point by the second distance, or the point apart from the excavation start point by the third distance in advance, and by setting the determination reference position to that of the bucket blade edge 132 e of the blade 132 or of the center of gravity of the vehicle body 110 in advance.

One embodiment has been described above in detail with reference to the drawings, but specific configurations are not limited to the above-described configurations, and various design changes or the like can be made. Namely, in other embodiments, the order of the above-described process may be appropriately changed. In addition, some of the process may be executed in parallel.

The controller 320 according to the above-described embodiment may be formed of a single computer, or the configurations of the controller 320 may be distributed among a plurality of computers, and the plurality of computers may cooperate with each other to function as the controller 320. For example, as shown in FIG. 10 , the controller 320 may include a remote controller 350 disposed outside the work vehicle 100, and an in-vehicle controller 360 mounted in the work vehicle 100. The remote controller 350 and the in-vehicle controller 360 may be able to wirelessly communicate with each other via communication devices 380 and 390. In addition, some of the functions of the controller 320 described above may be executed by the remote controller 350, and the remaining functions may be executed by the in-vehicle controller 360. For example, a process of determining the target design topography 70 may be executed by the remote controller 350, and a process of outputting a command signal to the work equipment 130 may be executed by the in-vehicle controller 360.

Alternatively, the operation device 310 may be disposed outside the work vehicle 100. In that case, the cab may be omitted from the work vehicle 100. Alternatively, the operation device 310 may be omitted from the work vehicle 100. The work vehicle 100 may be operated only by automatic control by the controller 320 without operation by the operation device 310.

Alternatively, as shown in FIG. 11 , current topography data may be generated from survey data measured by a surveying device 400 outside the work vehicle 100. As the external surveying device, for example, an aerial laser survey may be used. Alternatively, an image of the current topography 50 may be captured by a camera, and current topography data may be generated from image data obtained by the camera. For example, an aerial imaging survey by an unmanned aerial vehicle (UAV) may be used. In the case of the external surveying device or the camera, the updating of the worksite topography data may be performed at predetermined intervals or at any time.

The controller 320 according to the above-described embodiment creates a target design topography at the start of excavation, and controls the bucket blade edge 132 e to follow the target design topography, but the present invention is not limited to this configuration. For example, the controller 320 according to another embodiment may calculate a target displacement from a travel distance at regular timings based on a target displacement function, without creating a target design topography, and calculate a target height each time.

The work vehicle 100 according to the above-described embodiment is a bulldozer, but it is not limited thereto. For example, the work vehicle 100 according to another embodiment may be a motor grader.

According to the aspects, the control device can automatically control the pitch of the blade according to a working state of the work vehicle. 

1. A control system for a work vehicle including a vehicle body and work equipment that is changeable in height and pitch with respect to the vehicle body, the system comprising: a controller, the controller being configured to determine a switching point by referring to target displacement data indicating a target displacement of the height of the work equipment according to a movement amount of the work vehicle from a work start position, determine whether or not the work vehicle has reached the switching point based on the movement amount of the work vehicle from the work start position, and output a command to change the pitch of the work equipment upon determining that the work vehicle has reached the switching point.
 2. The control system for a work vehicle according to claim 1, wherein upon determining that the work vehicle has reached the switching point, the controller is further configured to output the command to change the pitch so as to tilt the work equipment rearward with respect to the vehicle body.
 3. The control system for a work vehicle according to claim 1, wherein the target displacement data indicates the target displacement that monotonically increases with an increase in the movement amount of the work vehicle within a range of 0 or greater and less than a predetermined value in a first region in which the movement amount of the work vehicle is less than a first distance, the target displacement equal to the predetermined value in a second region in which the movement amount of the work vehicle is the first distance or greater and less than a second distance, and the target displacement that monotonically decreases with an increase in the movement amount of the work vehicle within a range of 0 or greater and less than the predetermined value in a third region in which the movement amount of the work vehicle is the second distance or greater and less than a third distance, and the switching point is located within a range of the second region and the third region.
 4. The control system for a work vehicle according to claim 3, wherein the switching point is a point spaced from the work start position by the second distance.
 5. The control system for a work vehicle according to claim 3, wherein the switching point is a point spaced from the work start position by the first distance.
 6. The control system for a work vehicle according to claim 3, wherein the switching point is a point spaced from the work start position by the third distance.
 7. The control system for a work vehicle according to claim 1, wherein upon determining that a bucket blade edge of the work equipment has reached the switching point, the controller is further configured to output the command to change the pitch of the work equipment.
 8. The control system for a work vehicle according to claim 1, wherein upon determining that a position of a center of gravity of the vehicle body has reached directly above the switching point, the controller is further configured to output the command to change the pitch of the work equipment.
 9. The control system for a work vehicle according to claim 1, wherein the controller is further configured to acquire current topography information indicating a current topography of a work target, determine a target design surface displaced from the current topography in a vertical direction by referring to the target displacement data, and output a command to change the height of the work equipment along the target design surface.
 10. The control system for a work vehicle according to claim 9, wherein the target design surface is located below the current topography.
 11. The control system for a work vehicle according to claim 1, wherein the controller is further configured to cause the work equipment to be lowered so as to cancel out a change in a height of a bucket blade edge of the work equipment caused by the command to change the pitch of the work equipment.
 12. A method for controlling a work vehicle including a vehicle body and work equipment that is changeable in height and pitch with respect to the vehicle body, the method comprising: determining a switching point by referring to target displacement data indicating a target displacement of the height of the work equipment according to a movement amount of the work vehicle from a work start position; determining whether or not the work vehicle has reached the switching point based on the movement amount of the work vehicle from the work start position; and outputting a command to change the pitch of the work equipment upon determining that the work vehicle has reached the switching point.
 13. The method for controlling a work vehicle according to claim 12, wherein upon determining that the work vehicle has reached the switching point, the command to change the pitch so as to tilt the work equipment rearward with respect to the vehicle body is output.
 14. The method for controlling a work vehicle according to claim 12, wherein upon determining that a bucket blade edge of the work equipment has reached the switching point, the command to change the pitch of the work equipment is output.
 15. The method for controlling a work vehicle according to claim 12, wherein upon determining that a position of a center of gravity of the vehicle body has reached directly above the switching point, the command to change the pitch of the work equipment is output.
 16. The method for controlling a work vehicle according to claim 12, further comprising acquiring current topography information indicating a current topography of a work target, determining a target design surface displaced from the current topography in a vertical direction by referring to the target displacement data, and outputting a command to change the height of the work equipment along the target design surface.
 17. The method for controlling a work vehicle according to claim 16, wherein the target design surface is located below the current topography.
 18. The method for controlling a work vehicle according to claim 12, wherein the work equipment is lowered to cancel out a change in a height of a bucket blade edge of the work equipment caused by the command to change the pitch of the work equipment.
 19. A work vehicle comprising: a vehicle body; work equipment configured to be changeable in height and pitch with respect to the vehicle body; and a controller, the controller being configured to determine a switching point by referring to target displacement data indicating a target displacement of the height of the work equipment according to a movement amount of the work vehicle from a work start position, determine whether or not the work vehicle has reached the switching point based on the movement amount of the work vehicle from the work start position, and output a command to change the pitch of the work equipment so as to tilt the work equipment rearward with respect to the vehicle body upon determining that the work vehicle has reached the switching point. 